<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div {
            width: 100px;
            height: 100px;
            border: 1px solid red;
            float: left;
        }

        .dv4 {
            clear: both;
        }
    </style>
</head>
<body>
<div>div1</div>
<div>div2</div>
<div>div3</div>
<div class="dv4">div4</div>
</body>
</html>